Fluorescently labeled particles are being used extensively in a wide range of applications. By combining two or more dyes and by varying each of fluorescent dyes' concentration and/or the emission wavelengths of the dyes, it is possible to create an almost infinite number of fluorescently distinguishable particles. These particles can subsequently be used as markers in such diverse applications as combinatorial chemistry, diagnostics, e.g., DNA analysis, and industry uses, e.g., liquid labeling of fluids.
One such technology, which is currently available, uses polystyrene microspheres into which are absorbed precisely controlled quantities of two or more fluorescent dyes. This requires dissolution of the dye in an organic solvent, which can then be added to the microspheres, thus inducing swelling of the particle and absorption of the dye. The microspheres are then isolated from the dye solution and excess dye removed by a wash step. However, there are several drawbacks to this system. The first is that the wash step usually removes some of the dye from the beads, which makes it difficult to predict the exact amount of dye to be absorbed. Another problem is that placing these dyed microspheres in organic solvents results in leaching of the dye into the surrounding environment. Additionally, this technique requires that the dye be soluble in an organic solvent, which precludes the use of water-soluble particulate fluorescent materials. It would therefore be a significant improvement if methods were devised to encapsulate a precisely controlled number of soluble or insoluble fluorescent particles or substances within a stable shell material encapsulating them.
Encapsulation is a well-known technique in the art for protecting components that are sensitive to the elements, for providing controlled release of capsule ingredients, and/or to prevent dust formation by non-encapsulated particles among many other applications.
U.S. Pat. No. 5,879,920 issued to Dale et al., discloses multi-layered enzyme-containing composition, which is coated with a vinyl polymer. This composition, which is intended to be used as a laundry detergent, is useful for preventing enzyme-containing dust formation that may be allergenic to those who handle it. Among many other substances, fluorescent dyes are described as adjunct ingredients that may be added to the enzyme powder. However, no combination of fluorescent dyes is described or suggested. The only reason for using fluorescent dyes in detergents is to make laundered fabrics look brighter. Finally, the polymer shell of the enzyme granule must be readily soluble in an aqueous solution to release the enzyme and additive such as a fluorescent dye.
U.S. Pat. Nos. 4,724,094 and 4,341,997 issued to Song and Borrows respectively, disclose methods of preparing a fluorescent magnetic composition useful for inspecting and detecting cracks and various small defects in metal work pieces. The preparation of such fluorescent/magnetic particles is spread on the surface of a metal piece and defects are identified under ultra-violet light or “black” light. The manufacturing of these particles involves a plasticizer in order to effect a more complete encapsulation of fluorescent pigment and magnetic particle powder by film-forming resin. Composition made by the inventive method are described, as well as methods of using the composition in non-destructive testing of magnetizable work pieces. This invention is not functional without magnetic particles and it does not require more than one fluorescent dye.
U.S. Pat. No. 4,534,317 issued to Walsh discloses two types of encapsulated food pellets containing fluorescent dyes. The first type, which when eaten by fish, causes the water to fluoresce, the second type disintegrates spontaneously causing the water to fluoresce when not eaten by fish. By administering food containing both types of fluorescent dyes simultaneously, and measuring the ratio of their respective fluorescence intensities, a sensitive measure of feeding activity is achieved. While two fluorescent dyes are used in this invention they are not present in the same capsule and ultimately these dyes are meant to be released in the aqueous environment.
The encapsulation techniques are also used in an unrelated field of entrapping of living cells in tiny microcapsules, which are then introduced into a host organism as a means of delivery of biologically important factors produced by such cells. Examples of microencapsulation devices can be found in U.S. Pat. No. 5,182,111, issued to Aebischer et al.; U.S. Pat. Nos. 4,487,758, 4,673,566, 4,689,293, and 4,806,355, each issued to Goosen et al.; U.S. Pat. No. 4,803,168, issued to Jarvis, Jr.; U.S. Pat. Nos. 4,352,883 and 4,391,909, both issued to Lim; U.S. Pat. No. 4,298,002, issued to Ronel et al.; and U.S. Pat. No. 4,353,888, issued to Sefton. However, the purpose and scope of these devices are not related to the instant technical field and thus the interior of these microcapsules does not contain fluorescent dyes.
The present inventor has provided a novel principle of encapsulating fluorescent materials in light-permeable, environment-stable capsules capable of emitting at least two distinct fluorescent signals.